PROJECT SUMMARY This proposal seeks to leverage the emerging understanding of cellular and subcellular heterogeneity in opioid signaling for therapeutic discovery. The project develops new optogenetic and chemogenetic tools to achieve local control of opioid receptor activity and signaling in neural circuits and at a subcellular level of resolution. The proposal seeks to develop a versatile toolbox and provide proof-of-concept for in vivo precision pharmacology that have not yet been applied to the opioid system. The first phase (R61) is a high-risk technology enabling phase, based on combining our collaborative team's expertise in developing receptor-blocking intracellular nanobodies with established methods for conferring local control of nanobody concentration in the cytoplasm and specific membrane domains, using optogenetic and chemogenetic strategies that have already been validated but never before applied to opioid receptors. The R61 phase will develop these tools (Specific Aim 1) and validate them in neuronal culture and acute slice preparations (Specific Aim 2). These studies will provide not only proof-of-concept for in vivo precision pharmacology of opioid receptors, but also for G protein-coupled receptors as a class. We have set a specific series of milestones to evaluate progress, and to assess feasibility for advance to in vivo studies. If the milestones are successfully met, the second phase (R33) will apply the new tools to selectively target opioid signaling in neural circuits in vivo, focusing on analgesia, behavioral reinforcement and respiratory depression by clinically relevant opioid drugs. Mice are used as a well-established and relevant model (Specific Aim 3). These studies leverage the combined expertise of our collaborative team, and will establish powerful optogenetic and chemogenetic manipulations for the study of in vivo opioid function for the first time. Accordingly, the proposed studies to provide the first-in-class application of optogenetic and chemogenetic control to the opioid system in vivo, and they will explore a precision pharmacology of opioids based on location in neural circuits.